1. Field of the Invention
The present invention relates to a battery including a positive electrode, a negative electrode, an electrolyte, and a negative electrode current collector, at least part of which is formed as a rough surface, and also relates to a current collector and a negative electrode forming the battery.
2. Description of the Related Art
With progress in science and technology such as semiconductor technology, personal computers (PCs), mobile phones, and the like have been developed, and batteries utilized as power supply for electronic apparatus have been expected to facilitate handling of the batteries such as reduction in size and weight, and to exhibit excellent electric properties.
In view of such expectations, the following types of lithium-ion secondary batteries have been developed and have widely been used: a lithium-ion secondary battery having a graphite material that uses an intercalation reaction of lithium (Li) between graphite layers, or a lithium-ion secondary battery utilizing a carbonaceous material as a negative electrode active material to which lithium insertion and extraction into pores are applied.
In recent years, as increasing in power and time consumed for the electronic apparatus due to higher performance of the electronic apparatus, an increase in capacity and power generation of a secondary battery have been desired, and especially in capacity, property improvement has much been desired.
A battery including a negative electrode active material layer formed of a carbon material such as graphite may be difficult to greatly improve properties because a battery capacity of the negative electrode active material is about to reach the theoretical limit.
Increasing a thickness of an active material layer may improve battery capacity; however, if such thick electrode is formed of a smooth current collector typically used in the related art, peeling (detaching} strength decreases to deteriorate cycle characteristics of the battery. Further, if an amount of a binder is increased so as to control to lower peeling strength, load characteristic of the battery is lowered, thereby adversely affecting the cycle characteristics of the battery.
Japanese Unexamined Patent Publication No. 2003-7305 and Japanese Unexamined Patent Publication No. 2004-95474 disclose a method of fabricating a battery using a thin plate-form current collector that includes rough surfaces of both principal planes to control to lower peeling strength. Such a current collector having rough surfaces may improve peel strength without extremely increasing amount of the binder as described above. However, if such a current collector includes rough surfaces for lowering peeling strength, the current collector may become susceptible to crack or fracture.
While, a negative electrode active material containing silicon (Si), tin (Sn), metal lithium (Li), and the like has been examined. Since such a negative electrode active material can be inserted much lithium (Li) as compared a case with a carbon material, capacity of the battery may greatly be increased.
However, since the negative electrode active material containing silicon (Si) and tin (Sn) drastically changes its volume when charging and discharging the battery, the inner pressure increases to impose loads upon members located around the negative electrode active material. Further, in an electrode having an alloyed interface between a current collector and an active material layer, both the current collector and the active material layer may be cracked or fractured, resulting in lowering the battery capacity.